Many mobile machines used in industries such as mining, construction and farming utilize infinitely variable transmissions, such as a hydrostatic drive transmission. A hydrostatic drive transmission utilizes a hydraulic pump and hydraulic motor combination to provide continuously variable torque and speed to the drive train of the machine. Such transmissions can provide certain advantages over mechanical transmissions including improved fuel economy.
A potential issue with hydrostatic drive transmissions is that they can provide an operator with a different “feel” under certain operating conditions than a traditional mechanical transmission. One example of a circumstance where a hydrostatic drive transmission can provide a different feel is when an operator reduces the throttle when the machine is in motion. In such circumstances, the machine will coast a certain distance as the engine slows down. Machines with hydrostatic transmissions are typically configured to decelerate in the same manner regardless of the load or engine speed. As a result, a machine with a displacement controlled hydrostatic drive transmission will coast a similar distance no matter whether the machine is travelling on flat ground, uphill or downhill when the operator reduces the throttle. This can be unintuitive to an operator who may be used to operating machines with traditional mechanical transmissions that generally coast more when travelling downhill than they coast when travelling uphill or on flat ground.
U.S. Pat. No. 8,070,651 discloses a work machine coast control system with an infinitely variable transmission. The control system is configured to determine a driver demand regarding deceleration of the machine at a time of coasting accompanied by an accelerator releasing operation. The controller is further configured to control the transmission to decelerate the vehicle according to the determined drive demand regarding deceleration. The control system does not provide any adjustment of the coasting of the machine based on the slope on which the machine is operating.